Magnetoresistive memory devices, such as Magnetoresistive Random Access Memory (MRAM), use magnetization to store information. MRAM is a non-volatile memory device that uses magnetization to store information. Proposed in the early 1990s, MRAM is a relatively new technology compared to other forms of memory, such as dynamic random access memory (DRAM), electrically erasable programmable read-only memory (EEPROM), flash memory, etc. One major advantage of MRAM over its competitors mentioned above is its ability to combine various appealing attributes (e.g., non-volatility, speed) into one single memory solution.
In order to write information into an MRAM cell, a way to switch the magnetization within the cell is needed. In the current generation of MRAM, magnetic bits are written with the magnetic field produced by an electrical current. The spatial extended Orsted field may limit the recording density and the power consumption. An alternative method to manipulate the magnetization is to use a spin polarized current through the spin transfer torque (STT) effect. The STT effect originates from the exchange interaction between the transported electron and local magnetic moments. Magnetization switching has been realized in experiment. One difficulty for wide application of the current-induced switching is the high critical current density (on the order 107 A/cm2) that may be required to reverse, or switch, the magnetization. High switching current increases the overall power assumption. More significantly, it may prevent the reduction in size of the device when transistors providing large currents are needed.